Upgrades to the Newell Highway near Goondiwindi on the Queensland and New South Wales border are changing the way water flows across the flood plain and impacting farms and ecosystems, residents and experts say.
Pete Mailler, a farmer from Boggabilla, says his property experienced a record flood height from Whalan Creek on one side last week – and “equally extraordinarily” there was no flooding on the other side.
He says this is because the works at Newell Highway have raised the flood height and the speed of the flow east of the highway, while disrupting overland flooding to the west.
The upgrade between Mungle Back Creek to Boggabilla, jointly funded by the Australian and NSW governments, was officially opened on 13 April this year with the aim of improving the flood immunity of the highway corridor.
But in an open letter to Goondiwindi regional council, Mailler wrote that while the highway upgrades “may be excellent for keeping the highway open, they are inadequate in terms of managing the function of the flood plain and the safety of its townspeople”.
Mailler said that the rainfall event was not big enough to cause the magnitude of the flow that peaked on Saturday, indicating there was inadequate capacity in the causeways, culverts and bridges to clear the natural flooding due to the raising of the highway.
Prof Martin Thoms, a river science expert at the University of New England, said the highway upgrade between Goondiwindi and Whalan Creek would most likely have changed the hydrology of the flood plain.
“Any change to the distribution and flow of water in those flood channels would be of a major concern to local landholders,” Thoms said.
“The border rivers area has a very important flood plain ecosystem. If you interfere with flooding, it not only has an impact on agriculture, but a massive effect on local ecosystems.”
Thoms said the impact would not only be felt by farmers, but also the natural flood plain vegetation and animals, including native Murray cod and catfish, which depend on the natural flooding of the flood plain.
He said there had not been sufficiently detailed hydraulic studies of the border rivers area to allay the worries of local landholders.
Prof Jamie Pittock, from the Australian National University’s Fenner School of Environment and Society, said “embankments for transport infrastructure elsewhere in the Murray Darling Basin have been shown to exacerbate flood risk”.
A Transport for NSW spokesperson said the department “carried out extensive hydrology studies as part of the planning process to assess the upgrade’s impacts”.
“The upgrade involved the realignment of the Newell Highway, including new drains that were designed to be in the same locations as before the realignment to maintain water flow from one side of the highway to the other,” the spokeperson said.
“The upgrade was designed to achieve zero increase in flood levels on surrounding properties, unless otherwise agreed with affected landowners.”
Thoms said even if the drains were designed to be in the same locations as before, the raising of the height of the highway would likely still have an impact.
The flood modelling in the project’s submissions report acknowledged hydrological impacts in isolated locations on a small number of private properties near the highway.
Mailler said “the Roads and Maritime Service have decided … the net impact over the flood plain is negligible, but individually people will have to pay for that. That’s a gross injustice”.
Glen Smith, chairman of the organisation Border Rivers Food and Fibre, said the most recent flooding event was different to previous floods, in which equal amounts of water come from the Macintyre and Dumaresq rivers.
“This flood all the water came from the Dumaresq,” Smith said.
“I have no doubt the road would have had some kind of impact. They all do.”
Mailler said people east of the highway were more likely to get more flooding and people west of the highway were more likely to get less – and both would have an impact.
“If you stop the beneficial flooding on parts of the plain, [that] has significant impact on the ecology. What grows and how it grows.”
He said farmers sustain short-term crop losses after a flood event, but flooding underpins higher productivity in the long-term because it recharges the soil with moisture, sediments and nutrients.
“If we haven’t had the flood to fill the soil profile and dams, it predisposes us to drought conditions much faster.”
Lawrence Springborg, the mayor of the Goondiwindi region, said the council conducts a review after any major flood.
“This includes looking at possible impacts related to infrastructure changes.”
